The majority of coronary artery bypass grafting (CABG) and valve repair surgeries use cardioplegia and cardiopulmonary bypass (CP/CPB) to respectively arrest the heart and systemically circulate oxygenated blood. Hypothermic cardioplegia solutions provide myocardial protection during prolonged surgicallyinduced global ischemia that would otherwise prove lethal. However, cardioplegic arrest of the heart during surgery results in reversible ischemic injury that manifests in impaired contractility of viable myocardium and reductions in cardiac function (a.k.a myocardial stunning). In the majority of patients, this temporary impairment resolves quickly, however ~ 10 % can develop an associated cardiac low output syndrome lasting hours to days that greatly enhances the risk of mortality. Following CP/CPB, HSP27 and cryAB are phosphorylated on multiple residues. Current data in the literature suggests that the presence of nonphosphorylated sHSP is beneficial for post ischemic contractile function, and that ischemic insults (including CP/CPB) that induce phosphorylation of HSP27 and cryAB, and subsequent depletion of the nonphosphorylated sHSP pool, may play a role in myocardial contractile deficits or stunning. These studies are designed around the central hypothesis that preservation of non-phosphorylated HSP27 and cryAB levels will reduce or block CP-induced deficits in myocardial contractility. These studies will be performed in Aim I - Determine the upstream signaling mechanism of CP/CPB-induced HSP27 and cryAB phosphorylation. Aim II - Determine if overexpression of phospho-mutant sHSP's will reduce cardioplegia-induced contractile deficits in isolated myocytes. Aim III - Determine specific cardiac contractile signaling mechanisms associated with ischemia-induced alterations in sHSP proteins. Experimental interventions (pharmacological and genetic approaches) will be performed using isolated rat cardiomyocytes and Langendorff perfused hearts. If these Aims are successful, these studies will enhance our understanding of CP-induced contractile deficits, and suggest treatment strategies that could greatly improve current myocardial protection and reduce complications associated with cardiac surgery